typo3/cms-core security advisory

CVE-2026-0859: TYPO3 CMS Allows Insecure Deserialization via Mailer File Spool

CVE-2026-0859 is a medium-severity PHP object injection vulnerability in the PHP package typo3/cms-core (CVSS 7.8), published 13 January 2026. The advisory does not name a fixed version. Exploiting it needs a low-privilege user account.

medium 7.8 published 2026-01-13 · updated 2026-06-17

Affected versions: >= 10.0.0, <= 10.4.54
>= 11.0.0, <= 11.5.48
>= 12.0.0, <= 12.4.40
>= 13.0.0, <= 13.4.22
>= 14.0.0, <= 14.0.1
Fixed in: not stated
Newest release: 14.3.10
Severity: Medium · CVSS 7.8
Type: PHP object injection
CWE-502
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your typo3/cms-core version affected?

Run composer show typo3/cms-core in your project, then enter the version. We check it against this and every other known typo3/cms-core advisory.

Who can exploit CVE-2026-0859

Access: A normal, low-privilege user account in the app.
Position: The attacker needs local access to the server.

CVSS vector (scored by NVD): CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Your app is only exposed if it uses the affected part of typo3/cms-core. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-0859 in typo3/cms-core

Find the installed version: composer show typo3/cms-core. If you never required it yourself, composer why typo3/cms-core shows which package pulls it in.
Update it: composer update typo3/cms-core --with-all-dependencies.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "typo3/cms-core": "^14.3.10" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-0859.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for PHP object injection issues while the upgrade waits. None of it replaces the fix.

Never pass user-controlled data to unserialize() or to template rendering, and restrict who can edit templates or settings.
Put a web application firewall in front of the app and watch for new PHP files or admin users.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-0859 advisory

TYPO3's mail‑file spool deserialization flaw lets local users with write access to the spool directory craft a malicious file that is deserialized during the mailer:spool:send command, enabling arbitrary PHP code execution on the web server. This issue affects TYPO3 CMS versions 10.0.0-10.4.54, 11.0.0-11.5.48, 12.0.0-12.4.40, 13.0.0-13.4.22 and 14.0.0-14.0.1.

Description from the CVE record, via the NVD entry for CVE-2026-0859. Advisory title: “TYPO3 CMS Allows Insecure Deserialization via Mailer File Spool”.

References

GitHub advisory GHSA-7vp9-x248-9vr9 github.com
Typo3 security advisory typo3.org
Fix commit 3225d70 github.com
Fix commit 722bf71 github.com
Fix commit e0f0cee github.com

Other typo3/cms-core advisories

high CVE-2026-19418: TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool 2026-08-11
high CVE-2026-11607: TYPO3-CORE-SA-2026-019: Broken Access Control in Form Framework 2026-06-09
medium CVE-2026-49740: TYPO3-CORE-SA-2026-018: Insecure Deserialization in Core API 2026-06-09
high CVE-2026-49741: TYPO3-CORE-SA-2026-017: Privilege Escalation & SQL Injection in Form Framework 2026-06-09
low CVE-2026-49738: TYPO3-CORE-SA-2026-016: Broken Access Control in File Abstraction Layer 2026-06-09
medium CVE-2026-47352: TYPO3-CORE-SA-2026-015: Broken Access Control in Backend API 2026-06-09

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.